1. Field of the Invention
The present invention relates to a mobile communication system for transmitting broadcast data and/or multicast data to a mobile station, and to a mobile station used in such a mobile communication system.
2. Description of the Related Art
Conventionally, there is an MBMS (Multimedia Broadcast/Multicast Service) defined in 3GPP (3rd Generation Partnership Project) as the technique of transmitting broadcast data and/or multicast data to a mobile station.
In the MBMS, a service announcement is defined to include a “TMGI” (Temporary Mobile Group Identify). The TMGI is a service identifier for identifying broadcast data and/or multicast data available in each network.
A mobile station is defined to be able to receive desired broadcast data and/or multicast data by setting a TMGI for identifying the desired broadcast data and/or multicast data.
However, in the conventional mobile communication system, when a mobile station performs roaming between a plurality of networks, a means for acquiring the above mentioned TMGI in a roaming destination network is not defined.
Therefore, there is a problem in that the mobile station is not able to receive desired broadcast data and/or multicast data in the roaming destination network.
In other words, as illustrated in FIG. 1, when a mobile station MS#A which manages a service announcement #A including a TMGI for identifying broadcast data and/or multicast data available in an operator network A has performs roaming to an operator network B, means for acquiring a service announcement #B including a TMGI for identifying broadcast data and/or multicast data available in the operator network B is not defined.
Therefore, there is a problem in that the mobile station MS#A is not able to receive desired broadcast data and/or multicast data in the operator network B.
Further, as illustrated in FIG. 2, in the conventional mobile communication system, the TMGI is configured of a “roaming portion” for identifying an operator in the mobile communication system and a “local portion” for identifying a service(s) provided by the operator.
Thus, when the TMGI including the above-described roaming portion and local portion is utilized, the TMGI value becomes large, and processing load on a radio communication area between a radio controller and a mobile station to establish sessions for transmitting and receiving broadcast data and/or multicast data is increased.
Hence, in order to reduce the processing load on the radio communication area, the conventional mobile communication system is configured to identify the broadcast data and/or the multicast data only by the local portion in the same operator network.
However, the thus configured conventional mobile communication system may cause a problem in that the same local number may be assigned to different broadcast data pieces and/or multicast data pieces in a plurality of networks, and if a mobile station performs roaming with holding a TMGI for the roaming source network, it becomes difficult to specify broadcast data and/or multicast data available in the roaming destination network.